Piston ring assembly



July 19, 1966 R. F. GAMES PISTON RING ASSEMBLY Original Filed Nov. 19,1962 INVENTOR. fiaberiffiafizee,

. l I Z2 33 J7 JZ 29 a? United States Patent 3,261,612 PISTON RINGASSEMBLY Robert F. Games, Hagerstown, Ind., assignor, by mesneassignments, to Dana Corporation, Toledo, Ohio, a corporation ofVirginia Continuation of application Ser. No. 238,661, Nov. 19, 1962.This application Aug. 2, 1965, Ser. No. 479,040 12 Claims. (Cl. 277-140)This invention relates to piston rings, and, more particularly, to anoil ring assembly for an internal combustion engine.

This application is a continuation of my copending application SerialNo. 238,661, filed November 19, 1962, now abandoned.

It is -a primary object of this invention to provide a piston ringassembly including rails and a circumferentially expansible combinationspacer-expander, wherein the spacer-expander has improved deflectioncharacteristics.

It is another object to provide a piston ring assembly of the foregoingcharacter, having good oil drainage.

Still another object is to provide a piston ring assembly of theforegoing character, wherein the spacer-expander includes means forensuring alignment of its ends when in abutment.

A still further object is to provide a piston ring assembly of theforegoing character, wherein the spacerexpander exerts its expandingforce against the inner peripheries of the rails throughout the majorpart thereof and hence does not tend to gouge into the rails.

Other objects and advantages of the invention will become apparent fromthe following description taken in conjunction with the accompanyingfigures of the drawing, in which:

FIG. 1 is a plan view of a piston ring assembly embodying the invention;

FIG. 2 is an enlarged radial sectional view showing the assembly in agroove of a piston and confined within a cylinder;

FIG. 3 is an enlarged fragmentary perspective view of the assembly;

FIG. 4 is an enlarged fragmentary view of a part of the assembly; and

FIG. 5 is a fragmentary view of a strip of material from which part ofthe assembly is made.

In general a piston ring assembly for installation in a piston ninggroove, embodying the invention comprises a pair of annular cylinderengaging rails, and a combination spacer-expander for forcing the railsoutwardly. The spacer-expander comprises a plurality ofcircumferentially spaced axially extending support members, and aplurality of U-shaped spring members connecting the support members forcircumferentially expanding the spacer-expander. The ends of the arms ofthe spring members are connected to the support members, and the springmembers extend radially outward from the support members. To support therails adjacent their outer peripheries and to hold them axially spaced,an axially extended portion is formed on each spring member at itsoutermost portion. The cross section of each arm is varied throughoutits length by having the axial width of each arm decrease from theassociated support member and from the axially extended portion toward apoint substantially midway therebetween.

To engage the inner peripheries of the rails and to force themoutwardly, tabs are formed on the upper and lower sides of each supportmember, and the tabs pref erably slant inwardly from each supportingmember to force the inner peripheries of the rails against the sides ofthe groove. The tabs are of sufiicient length to extendcircumferentially in both directions beyond the support members in orderto engage the rails throughout the major part of their innerperipheries. If desired, the cirice cum-ferentially extending portionsof some of the tabs may be turned radially inward from the supportingmembers to prevent the spacer-expander from coming out of the pistonring groove when the piston is being inserted in the cylinder.

The spacer-expander is positioned between the rails with thecircumferential tabs engaging the inner peripheries of the rails andforcing them radially outwardly, due to the action of the springmembers. The inward slant of the tabs also forces the inner peripheralportions of the rails against the sides of the groove. The axiallyextending portions of the spring members are adapted to maintain theouter peripheries of the rails in axially spaced relation.

In greater detail, the piston ring assembly comprises a pair of annularrails 10 and 11, and a combined spacerexpander 12 (FIGS. 1, 2 and 3).The assembly is adapted to be positioned within an annular grove 13formed within a piston !14, and confined within a cylinder 15 of aninternal combustion engine. A passage 16 is also formed in the piston 14leading from the bottom of the groove 13 adjacent its lower side to theinterior of the piston for the purpose of draining oil from the groove13.

Each rail 10 and 11 is preferably made from a flat strip of metal suchas spring steel, and it is provided with a gap to permit it to expandradially. Each rail is preferably resilient and, by itself, exerts someoutward pressure against the wall of the cylinder 15.

The spacer-expander 12 is made from resilient sheet metal and it iscircumferentially expansible when it is confined within a cylinder withits ends in abutment. Its tendency to increase its circumferentialdimension causes it to exert aradially outward pressure against theinner peripheries of the rails 10 and 11 and force the rails against thecylinder wall. The spacer-expander also holds the rails adjacent theupper and lower sides 17 and 18 of the groove 13 with the innerperipheral portions of the rails bearing respectively against the upperand lower sides in sealing relation therewith.

The spacer-expander 12 comprises a plurality of circumferentially spacedsupport members 21 connected by U-shaped spring members 22. The ends ofthe arms of each spring member 22 are integrally connected to adjacentsupport members 21, and the spring members 22 extend radially outwardfrom the support members 21. An opening 23 is formed at substantiallythe center of each support member 21 for oil drainage purposes. Further,tabs 24 are formed on the upper and lower sides of the support members,the tabs 24 having sufiicient circumferential length to extendcircumferentially in both directions beyond the support members. Asshown in FIGS. 2 and 3, the tabs slant axially outward and radiallyinward from the support members. If desired, certain tabs 24 may haveend portions 26 turned radially inward. Thus, a tab on the upper andlower sides of every fifth support member 21 may have an end portion 26turned inwardly, for example, or an inturned end portion 26 may beprovided alternately on the upper and lower sides of spaced supportmembers. These portions 26 may be provided when the depth of the groove13 is relatively large or when the radial width of the rails 10 and 11is relatively small, in order to prevent the assembly from coming out ofthe groove at one side of the piston should the assembly be moved towardthat side during insertion of the piston into the cylinder.

Each U-sha-ped spring member 22 is formed with an enlarged axiallyextended portion 27 at its outermost portion to hold the rails inaxially spaced relation adjacent their outer peripheries. Further, thecross section of each arm of each spring member 22 is varied throughoutits length, the cross section decreasing from the ends of the arms andfrom the enlarged portion 27 by a decrease in the axial width of eacharm. As shown in FIGS. 3 to 5, each arm of each spring member issubstantially symmetrical throughout its length about a planeperpendicular to the axis of the spacer-expander and midway between thetwo sides of the spacer-expander. Each arm is also substantiallysymmetrical about a line extending axially through the midpoint of thearm. The cross section of each arm is designed to produce asubstantially uniform stress condition throughout its length when underload, due to the fact that the moment of inertia changes with the momentarm. In other words, the cross sectional area of each arm varies and, ateach section, the area substantially corresponds to the moment imposedon that section.

Each arm of each spring member may be considered two cantilever beams,one of the beams extending from the associated support member 2 1 to themidpoint of the arm and the other beam extending from the axiallyextended portion 27 to the midpoint of the arm. The support member 21and the axially extended portion 27 may be considered fixed points forthe two beams of each arm, and the midpoint of the arm may be consideredthe load point. To obtain a theoretically uniform stress condition ineach beam, the axial width of each beam should decrease linearly from amaximum width at the fixed point to zero width at the load point. Thus,each arm would resemble two triangles having their apexes in abutment atthe midpoint of the arm and their bases connected to the support member21 and the axially extended portion 27. Such a configuration isimpractical of course because material must be provided at the midpointof each arm to hold the two portions of the arm together. Thus, as shownin FIG. 5, the midpoint of each arm is widened axially to give itsuificient strength to hold the portions together under load. From itsmidpoint, each arm increases in axial width in both directions, and thesides of the arms approximate straight lines corresponding to the sidesof the above mentioned triangles.

Advantages of the described design of the arms of the spring members 22are that deflection of the spacer-expander is more satisfactory at thesame load than is obtainable by prior art spacer-expanders, and that theinstant spacer-expander provides a large amount of open space around thearms and through the spaces between the support members 21 for oildrainage. The small contact area between each portion 27 and the rails10 and 11, and the improved oil drainage reduce the possibility ofcarbon build-up and consequent unitizing of the assembly. Furthermore,the relatively large cut-away areas at the sides of the arms make itpossible from a manufacturing standpoint to provide thecircumferentially extending tabs 24. The foregoing advantages resultfrom an application of the uniform stressed beam theory to the design ofthe spring members 22.

The ends of the spacer-expander are provided with radial plates 28 and31 (FIGS. '1 and adapted to abut each other, these plates havingapproximately the same width as the support members 21. Means is alsoprovided for ensuring proper alignment of the ends and for connectingthe ends together, which may comprise an opening 29 formed in the plate28 and a circumferentially extending portion 32 formed on the plate 31and adapted to engage in the opening 29. The portion 32 is preferablyarrow shaped and includes barbs 30 which have a width slightly less thanthe diameter of the opening 29. When the ends of the spacer-expander arebrought together until the plates 28 and 31 abut, the pointed end of theportion 32 enters the opening 29 and guides the ends into properalignment. If the force applied to the spacer-expander to bring its endstogether is released, the barbs 30 catch on the plate 28 around themargin of the opening 29 and prevent the ends from becoming disengaged.When the spacer-expander is confined within a 4 cylinder, the plates 28and 31 abut each other, and the portion 32 prevents overlapping of theends.

The spacer-expander 12 is preferably formed from a fiat strip of sheetmetal which is punched to the form shown in FIG. 5. In punching from apractical standpoint, it would not be practical to make the sides of thearms, adjacent the support members 21, straight lines because of thetabs 24. The inner end of the recess between an arm which is connectedto a support member 21 and an adjacent tab 24 is preferably large enoughto permit the use of a punch having substantial body without any thinportions. To this end, the side of the arm at the line where it isconnected to the support member 21 is spaced from the tab 24 and filletsare provided in the corners to eliminate sharp corners on the punch tolessen the change of breakage at these corners. Since the arms are alsowidened adjacent their midpoints, the side edges of the arms are in theform of a smooth curve to facilitate manufacture of the expander. Suchsmooth curve conforms substantially to the theoretical configuration ofa uniformly stressed beam.

After the strip of metal is punched, it is bent along the dashed lines33 to form the spring members 22, and along the dashed lines =34 to fromthe tabs 24. The strip may also be bent along the lines 36 to form theradial end portions 26 of the tabs 24. Further, the strip is bent alongthe lines 37 to form the plates 28 and 3 1, and the longitudinal arrowshaped portion 32 is formed by bending along the line 38.

When the assembly is installed in the piston ring groove 13 and confinedwithin the cylinder 15 as shown in FIG. 3, the slant of the tabs 24 ofthe support members 21 force the rails 10 and 11 outwardly and the innerperiphcries of the rails against the upper and lower sides 17 and [18 ofthe groove 13- to produce side sealing. The outer peripheries of therails 10 and 11 are held in axially spaced relation by the enlargedaxial portions 27 of the spring members 22. Some dishing of the rails 10and 11 may occur when the assembly is in operation, as shown in FIG. 2.

During the operation of the engine containing the piston 14 and thecylinder 15, oil scraped off the walls of the cylinder 15, flows freelyaround the arms of the spring members 22 and through the spaces betweenthe support member-s 21, and through the openings 23 of the supportmembers 21, to the space behind the support members 21, and from thisspace into the passage 16.

Beside the previously described advantages of improved defiection andoil drainage characteristics due to the shape of the arms of the springmembers 22, the assembly has a further advantage in that the tabs 24engage the rails 10 and 11 around almost their entire inner peripheries.This large bearing area is provided by having the tabs extendcircumferentially beyond the support members 21. In constructions wherethe bearing surface between the rails and the spacer-expander isrelatively small, there is a tendency for the spacer-expander to indexitself or gouge into the inner peripheries of the rails, which tendencyis avoided by the present construction.

I claim:

1. In a piston ring assembly adapted to be installed in an annulargroove formed in a piston of an internal combustion engine and includinga pair of annular rails, an annular spacer-expander for forcing therails outwardly, said spacer-expander comprising a plurality ofcircumferentially spaced axially extending support members, and aplurality of U-shaped spring members connecting said support members forcircumferentially expanding said spacer-expander, each of said springmembers including a pair of arms connected at their outer ends by anintermediate portion which extends axially to support said railsadjacent their outer peripheries, the inner ends of said arms beingconnected to adjacent support members, and said spring members extendingradially outward from said support members, each arm of each of the saidspring members including an inner portion which decreases in crosssection from said support members to substantially the midpoint of saidarm, and an outer portion which increases in cross section fromsubstantially said midpoint to said intermediate portions, both of saidarm portions having a substantially uniform stress condition throughoutthe length thereof under load, and the area at each section of each ofsaid arm portions corresponding substantially to the moment imposed onthat section, said inner and said outer portions of each arm when takentogether approximating a pair of triangles with their apexes joined insaid midpoint region, the midpoint region of each of said arms having ashape and size just suflicient to maintain the structural integrity ofsaid arm, whereby each arm is designed and shaped both to produce asubstantially uniform stress condition throughout its length when underload, and to provide large cut-away areas at the sides thereof for goodoil drainage therearound, said spacerexpander being adapted to bepositioned between said pair of rails, and said support members havingmeans for engaging the inner peripheries of said rails and for urgingsaid rails outwardly.

2. The article of claim 1, wherein said arms are substantiallysymmetrical throughout their lengths about a plane perpendicular to theaxis of the spacer-expander and midway between the two sides of thespacer-expander.

3. The article of claim 2, wherein each arm is also substantiallysymmetrical about a line extending axially through the mid-point of saidarm.

4. In a piston ring assembly adapted to be installed in an annulargroove formed in a piston of an internal combustion engine and includinga pair of annular rails, the article comprising an annularspacer-expander for forcing the rails outwardly, said spacer-expandercomprising a plurality of circumferentially spaced axially extendingsupport members, and a plurality of U-shaped spring members connectingsaid support members for circumferentially expanding saidspacer-expander, each of said spring members having the intermediateportion of the U-shape extending axially to support said rails adjacenttheir outer peripheries and having the ends of its arms connected toadjacent support members, and said spring members extending radiallyoutward from said support members, each arm of each of said springmembers decreasing in cross section from said support members tosubstantially its midpoint and then increasing in cross section to saidintermediate portion and having a substantially uniform stress conditionthroughout the length thereof under load, and the area at each sectionof each of said arms substantially corresponding to the moment imposedon that section, each of said arms approximating a pair of triangleswith their apexes joined at said midpoint, the midpoint region of eachof said arms having a shape and size just sufiicient to maintain thestructural integrity of the arm, whereby each arm is designed and shapedboth to produce a substantially uniform stress condition throughout itslength when under load, and to provide large cut-away areas at the sidesthereof for good oil drainage therearound, said spacerexpander beingadapted to be positioned between said pair of rails, and said supportmembers having means for engaging the inner peripheries of said railsand for urging said rails outwardly.

5. The article of claim 4, wherein said means comprises tabs at theupper and lower sides of said support members, said tabs being adaptedto engage the inner peripheries of said rails and force the railsoutwardly and having end portions extending circumferentially in bothdirections beyond said support members, said end portions being axiallyspaced from the adjacent portions of said arms.

6. The article of claim 5, wherein certain of said tabs have endportions extending radially inward from said support members, and otherof said tabs extend solely circumferentially.

7. In a piston ring assembly adapted to be installed in an annulargroove formed in a piston of an internal combustion engine and includinga pair of rails, the article comprising an annular spacer-expander forforcing the rails outwardly, said spacer-expander comprising a pluralityof circumferentially spaced axially extending support members, and aplurality of U-shaped spring members connecting said support members forcircumferentially expanding said spacer-expander, each of said springmembers having the ends of its arms connected to adjacent supportmembers, and said spring members extending radially outward from saidsupport member, each arm of each of said spring members decreasing incross section from said support member and having a substantiallyuniform stress condition throughout the length thereof under load, andthe area at each sectionof each of said arms substantially correspondingto the moment imposed on that section, said spacer-expander beingadapted to be positioned between said pair of rails, and said supportmembers having means for engaging the inner peripheries of said railsand for urging said rails outwardly, both ends of said spacer-expanderincluding plates extending radially outward, said plates having aligningand interlocking means formed thereon, said aligning and interlockingmeans comprising a hole formed in one of said plates, and a portionformed on the other of said plates adapted to extend into said hole,said last named portion being pointed at its end for guiding saidportion into said hole, and said last named portion further includingbarbs adjacent its pointed end for retaining said portion within saidhole.

8. In a piston ring assembly adapted to be installed in an annulargroove formed in a piston of an internal combustion engine and includinga pair of rails, the article comprising an annular spacer-expander forforcing the rails outwardly, said spacer-expander comprising a pluralityof circumferentially spaced axially extending support members, and aplurality of U-shaped spring members connecting said support members forcircumferentially expanding said spacer-expander, each of said springmembers having the ends of its arms connected to adjacent supportmembers, and said spring members extending radially outward from saidsupport member, each arm of each of said spring members decreasing incross section from said support member and having a substantiallyuniform stress condition throughout the length thereof under load, andthe area at each section of each of said arms substantiallycorresponding to the moment imposed on that section, saidspacer-expander being adapted to be positioned between said pair ofrails, and said support members having means for engaging the innerperipheries of said rails and for urging said rails outwardly, both endsof said spacer-expander including plates extending radially outward,said plates having aligning and interlocking means formed thereon, saidaligning and interlocking means comprising a hole formed in one of saidplates, and a portion formed on the other of said plates adapted toextend into said hole, said last named portion being pointed at its endfor guiding said portion into said hole, and said last named portionfurther including at least one barb adjacent its pointed end forretaining said portion within said hole.

9. In a piston ring assembly adapted to be installed in an annulargroove formed in a piston of an internal combustion engine and includinga pair of annular rails, an annular spacer-expander for forcing therails outwardly and for holding the rails in axially spaced relation,said spacer-expander including a plurality of circumferentially spacedspring members tending to circumferentially expand said spacer-expander,said spacer-expander being adapted to engage said pair of annular railsat their inner peripheries and urge said rails radially outward and toengage the adjacent sides of said rails and hold the rails in axiallyspaced relation, said spacer-expander being split and having abuttingends, both ends of said spacer-expander including radially extendingplates, said plates having aligning and interlocking means formedthereon, said aligning and interlocking means comprising a hole formedin one of said plates, and a portion formed on the other of said platesadapted to extend into said hole.

10. In a piston ring assembly according to claim 9, wherein said lastnamed portion is substantially pointed at its end for guiding saidportion into said hole, and said last named portion includes at leastone barb adjacent its end for retaining said last named portion Withinsaid hole.

11. In a piston ring assembly according to claim 10, wherein said lastnamed portion includes two barbs adjacent its end for retaining saidlast named portion in said hole.

12. In a piston ring assembly adapted to be installed in an annulargroove formed in a piston of an internal combustion engine and includinga pair of annular rails, the article comprising an annularspacer-expander for forcing the rails outwardly, said spacer-expandercomprising a plurality of circumferentially spaced axially extendingsupport members, and a plurality of spring members connecting saidsupport members for circumferentially expanding said spacer-expander,said spring members being adapted to engage the adjacent sides of saidrails and hold the rails in axially spaced relation, saidspacer-expander being adapted to be positioned between said pair ofrails, and said support members having means for engaging the innerperipheries of said rails and for urging said rails outwardly, saidspacer-expander being split and having abutting ends, both ends of saidspacerexpander including a plate extending radially, said plates havingaligning and interlocking means formed thereon, said aligning andinterlocking means comprising a hole formed in one of said plates, and aportion formed on the other of said plates adapted to extend into saidhole.

References Cited by the Examiner UNITED STATES PATENTS 2,635,022 4/1953Shirk 277-140 3,004,811 10/1961 Mayfield 267-1.5 X 3,140,096 7/1964Rodenkirchen 277-141 FOREIGN PATENTS 1,123,357 6/1956 France.

LAVERNE D. GEIGER, Primary Examiner.

J. MEDNICK, Assistant Examiner.

1. IN A PISTON RING ASSEMBLY ADAPTED TO BE INSTALLED IN AN ANNULARGROOVE FORMED IN A PISTON OF OF AN INTERNAL COMBUSTION ENGINE ANDINCLUDING A PAIR OF ANNULAR RAILS, AN ANNULAR SPACER-EXPANDER FORFORCING THE RAILS OUTWARDLY, SAID SPACER-EXPANDER COMPRISING A PLURALITYOF CIRCUMFERENTIALLY SPACED AXIALLY EXTENDING SUPPORT MEMBERS, AND APLURALITY OF U-SHAPED SPRING MEMBERS CONNECTING SAID SUPPORT MEMBERS FORCIRCUMFERENTIALLY EXPANDING SAID SPACER-EXPANDER, EACH OF SAID SPRINGMEMBERS INCLUDING A PAIR OF ARMS CONNECTED AT THEIR OUTER ENDS BY ANINTERMEDIATE PORTION WHICH EXTENDS AXIALLY TO SUPPORT SAID RAILSADJACENT THEIR OUTER PERIPHERIES, THE INNER ENDS OF SAID ARMS BEINGCONNECTED TO ADJACENT SUPPORT MEMBERS, AND SAID SPRING MEMBERS EXTENDINGRADIALLY OUTWARD FROM SAID SUPPORT MEMBERS, EACH ARM OF EACH OF THE SAIDSPRING MEMBERS INCLUDING AN INNER PORTION WHICH DECREASES ION CROSSSECTION FROM SAID SUPPORT MEMBERS TO SUBSTANTIALLY THE MIDPOINT OF SAIDARM, AND AN OUTER PORTION WHICH INCREASES IN CROSS SECTION FROMSUBSTANTIALLY SAID MIDPOINT TO SAID INTERMEDIATE PORTIONS, BOTH OF SAIDARM PORTIONS HAVING A SUBSTANTIALLY UNIFORM STRESS CONDITION THROUGHOUTTHE LENGTH THEREOF UNDER LOAD, AND THE AREA AT EACH SECTION OF EACH OFSAID ARM PORTIONS CORRESPONDING SUBSTANTIALLY TO THE MOMENT IMPOSED ONTHAT SECTION, SAID INNER AND SAID OUTER PORTIONS OF EACH ARM WHEN TAKENTOGETHER APPROXIMATELY A PAIR OF TRIANGLES, WITH THEIR APEXES JOINED INSAID MIDPOINT REGION, THE MIDPOINT REGION OF EACH OF SAID ARMS HAVING ASHAPE AND SIZE JUST SUFFICIENT TO MAINTAIN THE